The present invention is directed to a method and an apparatus for reducing the standby power consumption of battery operated cordless or radio telephones.
Conventionally, it has been demonstrated that the power consumption of battery operated portable telephones can be reduced by operating these devices in a standby mode (also sometimes referred to as xe2x80x9cidle modexe2x80x9d) during the time between conversations when waiting for the subscriber to initiate a new call or to receive a new call from the network. The principal mechanism employed to reduce standby power consumption is to turn off the transmitter so that only the receiver is operating, i.e., listening to a designated network calling channel. However, modern hand-held telephones are so small that the available capacity of the small internal batteries is only sufficient to operate the receiver continuously for a few hours.
Accordingly, another method has been described and employed in various radiocommunication systems, e.g., systems designed in accordance with the European Global System for Mobile Communications (GSM) digital cellular system standard, to further reduce a receiver""s standby mode power consumption. This method involves pulsing the receiver on and off with a low duty factor. More specifically, the network is aware of the periods during which the receiver in any given portable station will be powered on so that the transmission of paging messages to a particular remote device can be timed to arrive at the remote device at those times. This technique is sometimes referred to as placing the remote device in a xe2x80x9csleep modexe2x80x9d whereupon it periodically xe2x80x9cwakes upxe2x80x9d to read the paging channel and to determine if a call is to be setup.
Portable telephones are, according to the GSM system specification, divided into sleep-mode groups either according to some of the digits of their telephone numbers or as designated by the network operator. As a simple example, those telephones having a number ending in 0 could belong to sleep-mode group 0; those ending in 1 to sleep-mode group 1 and so on. The network calling channel capacity is divided in time into a number of cyclically repeating periods (timeslots) corresponding to the sleep-mode groups. A call to a telephone is then transmitted only in a period corresponding to its sleep-mode group, when it is known to be awake. Upon waking, receiving such a message from the network and detecting that its own telephone number or identification number (ID) is being called, the portable receiver may stop pulsing and remain on continuously to receive further information and the portable transmitter may be activated to reply to the call when the subscriber accepts the call by, for example, pressing an appropriate button. In addition to waking up during its pre-assigned paging period to determine if it is being called by the network, a remote device may also need to periodically monitor the transmissions of neighboring base stations in order to ensure that it is listening to a preferred base station that provides a high quality connection.
As will further be apparent to those skilled in the art, it is desirable to maximize the amount of time that a remote device is sleeping to increase standby time associated with a given battery source. To accomplish this objective, it would further be desirable for a remote device to perform both of the aforedescribed tasks, i.e., listening for paging messages having its identification number and any further auxiliary functions, at the same time, e.g., when the remote device wakes up to read the paging channel.
However, as the complexity of radiocommunication systems generally increases to support increases in performance and capacity, the complexity and number of tasks performed by the remote devices to be able to properly detect and decode information transmitted by the system increase as well. Certain proposed wideband code division multipie access (W-CDMA) schemes require that remote devices perform, in addition to various types of time synchronization, certain other functions in order, for example, to identify the despreading codes associated with various base stations"" transmissions. These additional functions may require that the remote device read, in addition to its assigned paging timeslot(s) in each superframe, a plurality of different timeslots within the frame structure of a broadcast control channel, i.e., differently numbered timeslots. If, however, the remote devices are designed to xe2x80x9cwake upxe2x80x9d in the same numbered timeslot or timeslots in every superframe for paging purposes, it is then impossible for both the paging functions and the other, auxiliary functions to be performed at the same time, since the remote device would only be reading the same numbered timeslot in each superframe for both the control channel and the paging channel. Thus, the remote device will have to xe2x80x9cwake upxe2x80x9d for at least one other timeslot in each superframe in order to read the different numbered timeslot information needed for auxiliary processing. As mentioned above, this is undesirable since it increases the power consumption during standby mode.
Accordingly, it would be desirable to provide systems, remote devices and techniques which are designed to reduce standby power consumption by permitting the remote device to perform both its paging functions and other auxiliary functions (e.g., base station code identification functions) during its assigned paging timeslot(s).
These and other limitations and drawbacks of conventional sleep mode and paging techniques are overcome according to exemplary embodiments of the present invention which make it possible for the remote device to acquire information from differently numbered timeslots on a control channel, while only awakening for the minimum amount of time needed to read its assigned paging timeslot(s). According to one exemplary embodiment, this can be accomplished by providing a different number of timeslots per superframe in the paging channel than in the control channel. In this way, an incremental timeslot offset between control channel superframes and paging channel superframes is created. Thus, when a remote device awakens to read its assigned paging timeslot(s) it can, at the same time, read a concurrently received control channel timeslot. Due to the created offset, the concurrently received control channel timeslot will change from superframe to superframe, even when the remote station is reading the same paging timeslot relative to the paging channel superframe structure.
According to another exemplary embodiment of the present invention, reading information on differently numbered timeslots of a control channel while minimizing powered on time in standby mode can be accomplished by remapping the remote device to different paging groups and taking advantage of any additional awake time. By remapping the remote device to different paging groups, the remote device will be able to read differently numbered timeslots on the control channel. Moreover, if a remote device needs to be awake for more time than just its assigned paging timeslot (e.g., to perform channel estimation), then this additional time can also be employed for reading differently numbered timeslots on the control channel.
According to yet another exemplary embodiment, the assigned initial timeslot associated with any given remote device can be varied from superframe to superframe to provide the remote device with an opportunity to read the information in different control channel timeslots when it awakens to listen for paging messages.